如图，C、D分别是一个湖的南、北两端A和B正东方向的两个村庄，CD=6km，且D位于C的北偏东30°方向上，则AB的长为（　　）

    Last year, some groups of students in their community (社区) made a survey about "How do people spend their free time?" The following diagrams show some results of it:
Diagram (1): Hours for people of different ages who surf the Internet in a week.

Diagram (2): Different days people go to the library. (library attendance)

Diagram (3): Different programs people like.

根据上面三个图表内容，选择正确答案。